1. Field of the Invention
This invention relates to a sliding or movable stopper for an injector or syringe used for dosing a human body or animal with a liquid medicament.
2. Description of the Prior Art
An injector is generally constructed of a barrel 48 of a glass or thermoplastic plastic, a sliding stopper 41 of a glass, rubber or thermoplastic elastomer and a plunger rod 47, as shown in FIG. 5. A combination of a glass barrel and glass sliding stopper has rarely been used recently, but a combination of a glass barrel and elastomer sliding stopper has been used for a syringe additionally serving as a container to be filled with a liquid medicament and a combination of a plastic barrel and elastomer sliding stopper has ordinarily been used for a throwaway disposable syringe. FIG. 4 is a cross-sectional view of an elastomer sliding stopper 41 of the prior art, in which a sliding part on the inner wall of a barrel 48 has annular protrusions 45a and 45b which are contacted with the inner wall of the barrel.
Syringes or injectors must be germ-free and dust-free in view of their purpose and must have special physical properties such as liquid tightness, gas tightness and sliding property, which depend on the degree of contacting of the inner wall of a hard barrel with a sliding stopper consisting of an elastic material. Since every barrel has different straightness, smoothness and circular deformation of the inner wall and some errors in dimension and shape corresponding to the position, i.e. front part, central part and rear part, however, the above described degree of contacting in differs every barrel and every position of a barrel.
In order to correct such a differences, the diameter of a sliding stopper is ordinarily made larger than the average inner diameter of a barrel and the degree of contacting is increased to improve the liquid tightness and gas tightness. In this case, however, it is required to coat the sliding part with a silicone oil as a lubricant to make up for the thus lowered sliding property and the use of this silicone oil causes a problem of fine particle contamination of a medicament to be dosed.
To remedy this situation , the inventors have proposed a high quality syringe in which no silicone oil is required by laminating the surface of a sliding stopper with a fluoro resin and the contamination due to the silicone oil can thus be prevented, as disclosed in Japanese Patent Laid-Open Publication Nos. 243122/1986 and 139668/1987.
The laminated sliding stopper the inventors have proposed can completely solve the problem of contamination by a silicone oil as described above, but in a case where there are errors in dimension and shape of the inner wall of a barrel, the laminated sliding stopper cannot fully follow up the surface fluctuation as compared with non-laminated sliding stoppers, thus often resulting in deterioration of the sealability or tightness during sliding, i.e. using the syringe. Furthermore, the laminated sliding stopper often undergoes lowering of the tightness, in particular, in the case of twistdrawing when aspirating a liquid medicament or in the case of slant pushing when injecting a liquid medicament.